Permanent memory structure with thermo-optical writing and optical reading and writing process in such a structure

Abstract

The invention relates to a permanent memory structure supported by a moving substrate. This substrate is formed by two metal layers (9, 10) vacuum-deposited on the relatively inexpansible substrate (1). One of the two metal layers is very expansible (9), while the other layer (10) is relatively inexpansible, but ductile. During inscription by the laser beam, the beam energy absorbed by the layers (9, 10) produces an elongation of the expansible layer (9), which deforms the ductile layer (10) by stretching it beyond the elastic limit. There is a permanent deformation of the two-layer assembly, without perforation. Particular application to optical disks.

What is claimed is: 
     
       1. A permanent memory structure with thermal writing or inscription and optical reading, supported by a forwardly moving substrate, wherein the substrate is made from a material with a low expansion coefficient and the inscribable layer deposited on the substrate comprises at least one double metal layer having a high differential expansion coefficient between the very expansible material of the first metal layer and the only slightly expansible, but ductile material of the other metal layer. 
     
     
       2. A memory structure according to claim 1, wherein the very expansible metal layer is placed between the substrate and the relatively inexpansible, but ductile metal layer. 
     
     
       3. A memory structure according to claim 1, wherein the relatively inexpansible, but ductile metal layer is placed between the substrate and the very expansible metal layer. 
     
     
       4. A memory structure according to claim 1, wherein the very expansible metal layer is made from the following metals: Cd, Zn, Tl, Mg, Al, Mn, Ag, either individually or in alloy form. 
     
     
       5. A memory structure according to claim 1, wherein the relatively inexpansible metal layer is made from the following metals: Mo, Zr, Ti, Ta, Cr, Pt, individually or in alloy form. 
     
     
       6. A memory structure according to claim 1, wherein inscription or writing is in the form of a permanent deformation of the ductile layer, said deformation exceeding the elastic limit, but being below the breaking limit of the ductile layer. 
     
     
       7. An inscription or writing process in a memory structure according to any one of the preceding claims wherein the inscription layer is deformed by a laser beam, whose thermal energy is absorbed by the double metal layer and, in the ductile layer, is transformed into a mechanical deformation by elongation beyond the elastic limit, but less than the breaking limit.